Electrocardiograph



April 13, 1954 w, E. GILSON ET A1.

ELECTROCARDIOGRAPH 4 Sheets-Sheet l Filed May 2, 1950 NNN. QW

April 13, 1954 w. GILSON ET A1. 2,674,992

ELECTROCARDIOGRAPH Filed May 2, 1950 4 Sheets-Sheet 2 April 13, 1954 w. E. GILSON ET Ax. 2,674,992

ELECTROCARDIOGRAPH 4 Sheets-Shea 5 Filed May 2, 1950 April 13, 1954 W. E. GlLsON ET AL 2,674,992

ELECTROCARDIOGRAPH 4 Sheets-Shee 4 Filed May 2, 1950 Patented Apr. 13, 1954 reussi?.

ELECTROCARDIOGRAPH Warren E. Gilson, Madison, and Sherrill K. Rasmussen, Milton, Wis., assignors to The Burdick Corporation, Milton, Wis., a corporation of Delaware Application May 2,1950, Serial No. 159,608

3 Claims.

The present invention relates to electrocardiographs primarily `although certain aspects of the invention may be applied to other devices Where similar problems are encountered.

Essentially an electrocardiograph is a heart diagnostic instrument through which a tape is pulled continuously when the device is in operation and upon which tape a curve is drawn to indicate substantially the electric potential changes between Vdifferent parts of the body due to the heart action.

Essential elements of such a device, therefore, are the tape storing, handling and pulling mechanism, the Vtape marking device, a high gain amplifying system for actuating the marking devi-ce, a plurality of electrodes for attachment to the patient, together with their attendant cables, and a switching arrangement ior connecting these cables in different combinations to the amplier. Most of these components are assembled within a chassis and a Ycase is provided to house the equipment;

One of the objects of the Ipresent invention is to provide such an instrument with an improved -tape handling mechanism Iwhich is particularly advantageous when used with a paper base tape of the type now commonly employed.

An additional Objectis to provide an arrangement which automatically places upon the tape when the instrument is in operation an indicia which is permanent and which tells the operator Whether or not the tape `was being pulled at a uniform and proper speed, and which of certain combinations ci electrodes were used for obtaining the curve on the tape.

Yet another object is to combine with the mechanism last mentioned' above a novel additional marking scheme for placing upon the tape indicia to indicate unusual combinations of electrodes beyond the capacity of the automatic mechanism to indicate.

In amplication of the above it is `more specifically an object of the present invention to provide mechanism for marking the tape with a second line, that is in addition to the line indicating the heart potential, this second line indicating which combinations o electrodes were used in obtaining the heart action curve and also for indicating by means o" pips in the second line at regularly spaced intervals whether or not the tape handling and pulling mechanism is or was Auncticming properly.

Still another object is to provide a novel and convenient tape handling and pulling mechanism which is easy to thread.

And another object is to provide a novel arrangement in conjunction with the tape handling mechanism which keeps the tension of the tape passing through the machine substantially uni- -iorm regardless of changes in the characteristics of the tape due to changes in humidity or age or spool diameter.

Other objects and advantages Will'become apparent from the following description of a preferred embodiment of our invention which is illustrated in the accompanying drawings, in which:

Fig. 1 isa side View of an electrocardiograph embodying the present invention, the mechanism being removed from the case so as to show its essential structure. In this view portions of the apparatus, suchv as' the amplier, for instance, have been eliminated since their construction is not essential to an understanding of the present invention;

Fig.' 2 is a plan View of a `portion of the tape used by and marked in the machine shown in Fig. l;

Fig. 3 is a top view of the electrocardiograph illustrated in Fig. l;

Fig. 4 is a vertical transverse sectional view which may lbe considered as taken substantially along the line ll--l of Fig. 1 in the direction indicated by the arrows;

Fig. 5 is a longitudinal verti-cal sectional view which may be considered as taken substantially along the line 5-5 of Fig. 3 in the direction indicated by the arrows;

Fig. 6 is a top fragmentary view drawn to larger scale of a portion of the mechanism illustrated in Fig. 3 so as to show its construction and operation in greater detail;

Fig. 7 is a vertical fractional sectional View of a portion of the mechanism drawn to large scale so as to illustrate `a portion of the linkage mechanism for marking certain indicia upon the tape passing through the device; and

Fig. 8 is a detail vertical longitudinal sectional view which may be considered as taken substantially along the line 3 8 of Fig. l in the direction indi-cated by the arrows.

The electrocardiograph which forms the subject of the present invention has its working mechanism largely enclosed lwithin and supported by rectangular generally open framework. It comprises a flanged bottom plate iiil supported upon rubber bumpers or feet 112. This bottom plate is connected to upstanding sheet metal side members hl with portions cut out therefrom to reduceweight and to provide openings as needed.

At the `top the frame is braced `by longitudinal and transverse struts I6 and carries a top plate I3. Since the frame per se is not the subject of the present invention and any suitable frame will do, the specific frame here shown need not be further described.

Within this frame and at one end thereof the left end as seen in Figs. 1 and 3 there is a sepa rate subframe upon which the galvanometer and tape pulling and handling mechanism is mounted. This subfrarne is made up of a rigid cast` base somewhat less than half the width of the bottom plate I0 which is fastened by screws thereto. The casting 2li carries at one side an upstanding plate 22 about half as long as the chassis at about the middle thereof. This plate is arranged near one end of the frame and extends from top to bottom. It, together' with a similar but longitudinally shorter outside plate 24, bolted to the other side of the subirarne 2E, acts to support the tape handling mechanism, as an integrated rigid structure.

A horizontally and transversely disposed tape supporting tube 2d is mounted upon the vertical plate 22 low down and toward the left, as seen in Figure l. It has an external diameter slightly smaller than the internal diameter of the spool 21 upon which a roll 28 of recording tape 29 is wound so that the spool of tape may be easily slipped over the tube 2li. Once in position it is retained by a spring loaded detent which projects from the end of the tube 2E and snaps upwardly across the end of the tape spool 2l.

passes rearwardly over a horizontal, transversely disposed pin 32. This pin projects from and is fixed tothe plate 22. The pin per se is best obsimilarly is provided with a collar or enlargement 36 of approximately the same diameter as the head 34. 'Ihe stem portion of the pin 32 between the collar and the head 34 is slightly longer than the width of the paper tape 29 which passes thereover.

The tape is coniined against the pin 32 between the head and collar by a keeper or tensioner 38. This tensioner is made up of a fiat plate 40 with portions of its side edges bent over at approximately right angles to form nanges 42 to give it greater stiiness. It rests against the upper surfaces of the head 34 and collar 36 near its right hand end and has this extremity bent downwardly to form a tab 44 which lies just beyond the pin 32. The paper tape is therefore caused to pass over the pin 32 and thence downwardly around the end of the tab 44, and thence sharply upwardly in a manner to be pointed out presently in greater detail.

The left hand end of the keeper lit or more properly these ends of its side flanges 42 are pivoted to ra horizontal cross pin 46 which has its ends xed in the vertical plate 22, and an L- shaped subframe member 438 which is supported in a manner to be discussed presently. The tensioner 40 is therefore free to Divot upwardly and downwardly about the pin 45. At its left hand end beyond the cross pin 4G the end portion of the plate 40 is bent downwardly at about right angles and thence to the right to form a transverse spring seat or abutment 5E?. .A pair of side by side coil springs 52 have their left ends fixed to a transverse rod 54 also secured to the vertical plate 22. 'I'hese springs pass downwardly around the abutment 50 and thence upwardly where their opposite ends 55 are hooked through openings in the plate 40 well beyond the cross pin 48. Since these springs are under tension they will resiliently hold the free end 44 of the paper tensioner 40 against the pin 32. A transverse pin 51 projects from the rod 54 and serves as a handle to rotate the rod 54 to adjust the tension of the springs 52 and hence the paper speed which should be constant with very narrow limits.

An L-shaped sheet metal bracket 58 has one end bent over and secured to the lower surface of the plate 40 as by rivets 60. 'I'his bracket extends downwardly in a plane parallel to the backing plate 22 from the tensioner 38 and thence curves toward the right as seen in Fig. 5 into a position somewhat beyond the pin 32, and is provided at its end with a transverse headed pin 62. This headed pin 62 lits a longitudinal slot 64 in a downwardly extending sheet metal arm 66 which is provided for pulling upwardly on the pin 52 so as to lift the end of the arm 58 and thence to raise the tab 44 of the tensioner 38 into a position well above the cross pin 32. The purpose being to facilitate threading of the tape 29 through the tape pulling mechanism as will appear subsequently.

The Lshaped side support bracket 48, previously referred to, is in the same plane as the side plate 24 and may be considered as an extension of this plate with a curved slot 49 formed thereetween. It is disposed with one arm of the L in a generally horizontal position, this portion of the arm being fixed by screws lil to a pair of parallel transverse rods 54 and 68 which are secured at their opposite ends to the vertical plate 22. The right hand portion of the bracket 48, indicated by the numeral l2, inclines upwardly toward the right and has its upper end secured by a pair of screws 'I4 to the outward end of a horizontal transversely extending rectangular bar '.'5 (Figs. 5 and 3) anchored at its inner end to the plate 22. This transverse bar I6 also carries a dull knife edge 18 secured thereto in face to face relation with the thin edge uppermost.

The tape 29 is passed over this edge and thence downwardly around a driving roll which will be described more specifically subsequently. At present it is suiiicient to note that it is journalled to rotate about a horizontal transverse axis which extends between the vertical plate 22 and the bracket 48, and that the rotating axle for the roll 80 passes through the plate 22 where it is connected to the output shaft of an electric motor and speed reducing gear box unit 82 mounted upon the back of the plate 22. This motor is of the synchronous type and drives the roll 80 at a constant speed of 30 revolutions per minute.

The tape is pressed against the driving roll 8i) by an idling roll 34 which is comprised of a layer of soft rubber formed about an axle 86 journalled at its ends in a pair of overhanging arms 88. These arms which are parallel are formed of sheet metal and are spaced apart a distance somewhat greater than the width of the paper tape 29. They extend from the idling roll 84 in a generally left hand direction for a short distance and thence upwardly and toward the right to a position somewhat above the knife edge 'I8 and thence to the right and downwardly such that their opposite ends are pivoted to a cross pin 9i! which extends between the plates 22 and 24. The two generally J-shaped arms 88 are cross braced at intervals to maintain spacing and approximate alignment by means of transverse rods 92,` 0411 and 96. Onev of these rods. d, which is spaced. somewhat` tol the left of the top of the knife edge 18, is formed of an electrical insulat ing material, since it is also usedto manipulate a pair of electrically heatedv styluses and might shorty circuit the stylus leads were itformed of metal. The construction and arrangementv of these styluses will be pointed out presently.

The pivotal connection between the arms 68 and thevrod :it are formed by a pair of slots t3 in the'right hand ends ofthe arms E8 which straddle the rod ist. The slots have a width to fit therod 9@ and a length such that arms 83 and roller dit can move backwa..idly and forwardly as well as pivotally relatively to the rod 90. These slotsincline upwardly and to the left so that as the right hand ends of the arms slide toward the right, they also move downwardly with respect to the rod 90.

At a point somewhat below and to the left of the rod Si), the arms S8 are connected to the ends of a pair of coil springs |530 which extend downwardly to the right and have their opposite ends attached to screws isf: fixed in the plates 22 and 24. The angle of action of these springs is such as to tend to cause the free ends of the arms 5S, that is the ends attached to the idling roll di, to be swung downwardly and to slide toward the right under the influence of these springs. The

extreme lower free ends of the arms t8' below the i roll 84 are bent sharply outwardly to form tabs |04 which rest against the sides of a pair of short transverse pins or abutments 10S` xed to the plates 22 and 48. The action of these tabs against the pin |06 limits the downward movement of the idling roll 84 such that further action of the springs |00 causes a sliding movement of the arms toward the right, thus squeezing the idling roll 86 against the face of the paper tape opposite the driving roll 80;

After the tape has passed between the rolls 00 and 84, it crosses a small table |08 supported by the bars 54 and 68 previously referred to which directs the tape to the outside of the machine at ||0. The tape is preevnted from bunching up on the table |08 by an overlying transparent plastic guard H2 which is hinged at its outward end to pins ill carried in small brackets It fixed to the top of the table |08. Because of this hinge connection the inner end of the guard may be tilted upwardly to facilitate threading the tape thereunder after which itmay be pushed down into the position shown in Figs. 5 and 2, for instance, As shown in Fig. 3 the central portion of the guard ||2 in theregion of its outward end may be out away as indicated at H3.v to4 permit free insertion of the operators nngerv to facilitate alignment of the end of the tapeA across the table and beneath the guard H2.

This tape handling mechanism insures the tape moving smoothly'at proper speed and since the tensioning apparatus works against an intermediate portion of the tape, the tension is not affected by the size of the roll and thus gives more accurate control than is customary.

To the right and slightly below the insulated spacer 941 a shaft extends transversely between the vertical plates 22 and 2d. It is `iournaled in these plates and is provided with a knob. |22 at its outward end beyond the plate 2d by means of which the shaft |20 may be manually rotated. This shaft at about its midpoint carries a cam |24 best seen in Fig. 5 which is secured thereto by means of set screws |23. The cam is in the free position as shown in Fig. 5 with the cammingfsurface- |28 out of contact with the spacer 9'4. This camming surface is generally spiral in form so that as the shaft |20 is rotated in a clockwise-direction, the camming surface |28 is brought against the spacer 94 and with continued rotation forces the spacer 94 upwardly and to the left.` The extreme end of this camming surface. is formed to provide a stop |3il which is brought against the under surface of the spacer 04 and limits the rotational travel of the cam |24.

The angle made with the horizontal by a line through the spacer 94 and the rotatable shaft |2 is less than that made by the spring |00, with the resultthat when the knob |22 is rotated in a clockwise direction and the cam surface |20 is brought against the spacer 94, further rotationl at first causes the arms 88 and roller 84 to be shiftedtoward thel left without the roller being appreciably lifted. This movement is accommodated by the slot Swhich embraces the pin 90. After a predetermined degree of travel of the arms to the left the lower ends of the slots Slt` impinge against the pin 90 and further travel ofthearms 88 to the left is inhibited. Upon additional rotation of the knob lifts the spacer 04 arcuately, the center of rotation being at the pin 90. When the stop |33A is brought against the spacer 04 theA arms 88 have been lifted into the phantom line position shown in Fig. 5. Since the portion of the camming surface |28 immediately adjacent the stopV |30 is flat or slightly reentrant with respect to the shaft |20, the cam is locked with the arms 88 in the uppermost position. That is, once the arms have been raised and the stop |30 lhas been brought against the spacer '94, the spring |00 will not return the arms 88 to their lowermosil position. This over-center action of the cam enables the knob |22 to be released after the arms are raised so that both hands can be used for thread ing the tape through the machine.

Zit will be seen that the idling roller 84 presses the tape 20 against the driving roll $0 well below its center line, thereby insuring good frictional drivingv engagement and that the linkage just described automatically insures that simple rotation of the knob |22 in a clockwise direction will shift the idling-roll 84 approximately hori- Zontally to the left well clear of the roll 80 before lifting it, thereby preventing binding and scufling of the tape.

rThe rock shaft |20 also carries an arm |32 which inclines downwardly and to the left and at its lower end is connected by a pin |554 to the upper end of the link E8 previously referred to.

Thus it will be seen that when the knob |22 is rotated in a clockwise direction so as to cause the cam |24 to lift the roller 85, this rotational movement of the shaft |20 also causes the arm |32 to lift the link t6. After this link has been lifted a short distance the lower end of the slot Mis brought against the headed pin |52 so that continued rotation of the shaft |20 causes the link 6E to lift the right hand end of the arm 58, thereby lifting the tensioner 3B away from the cross pin 32. In its uppermost position the connection between the arm |32 and link 55 passes the centerline of the shaft |20 so that the actionV of the springs 52 do not tend to reverse the'rotation of the knob |22 when it is` released. To permit this thel upper'end of the link 56 is odset somewhat to the right so as to avoid its impinging against the shaft |20.

As best seenin Fig. 3, the right hand end Aof the base casting 20 supports a galvanometer |36 which is energized by the amplifier circuit of the device. The responsive element of this galvanome-ter is connected to a rotatable shaft |38 which projects vertically at the top of the galvanometer and is there connected to a stylus, indicated generally by the numeral |40'.

This stylus consists of two arms |42 formed of spring wire which in general form a sharply acute triangle with the base ends connected to a transversely extending insulating strip |44. The center of this strip carries a Din |46 which projects to the right and through a transverse hole in the end of the shaft |38 and is there secured :by a set screw in the end of the shaft. At the left hand end of the stylus the two arms |42, one of which is a half inch or so longer than the other, are connected to the two ends of a short strip |48 of electrically heated resistance ribbon which is horizontally disposed and rests against the top surface of the knife edge 18. The two arms or wires |42, -which are insulated from each other therefore serve both to support the heating element &8 and act as the electrical leads for conducting current through this ribbon. Although it is not shown in the drawings, the right hand ends of the wires |40 are A.soldered to flexible pigtaii leads which are connected to any suitable source of electric power at comparatively low voltage.

These wires or arms |42 lie directly above the insulating spacer 94 which conects the idler roll arms 88. Thus, when the knob |22 is rotated and lifts the arms 88 and spacer 94, this spacer will .be brought against the lower surfaces of the wires |112 at a point Liust behind the resistance ribbon |48. The result is that the ribbon |48 is lifted from the vicinity of the knife edge 18 at the same time that the roller 84 is moved well away from the driving roll 88 and simultaneously with the raising' of the tensioner 38 from the cross pin 32.

To load the instrument with tape therefore the roll of tape is inserted with its spool opening over the top of the detent 3G and with the inside end of the roll inclined downwardly. Then as the outer end of the roll is moved downwardly to a horizontal position depresses the'detent 30 and slips easily over the tube 2S with the detent 30 held down by the inner surface of the spool 21. The .roll is pushed straight inwardly until the dctent 35 snaps upwardly beyond the end of the spool 21. The spool should be inserted so that the tape pays off of the roll from the top in a direction toward the right with the sensitive surface of the tape down.

With the knob |22 rotated as far as it will go in a clockwise direction thereby clearing the tape path through the mechanism, the tape is passed to the right over the pin 32, up through the slot 49, over the upper surface of the knife edge 18, and thence downwardly between the driving roll 80 and the idling roll 84. The end is then passed across the table |88 beneath the guard I2 and out of the machine at I8. To facilitate the latter part of this operation, the guard ||2 should be tilted upwardly as previously explained, and the operators finger should be passed into the tape opening at the left hand edge of the machine into the clearance space provided in the guard ||2 at |18. The knob |22 is then rotated in a counterclockwise direction so as to lower the tensioner 38 into position against the pin 32 while simultaneously lowering the ribbon |48 of the stylus |40 against the portion of the tape passing over the knife edge 18. At the same time of the tape.

8 the idling roll 84 clamps the tape against the driving roll 80. This completes the threading operation.

When the machine is placed in operation the driving roll 80 revolves in a counterclockwise direction thereby pulling the tape from the roll 29 and passing it to the left and across the table |08 and out of the machine. Since the tape 29 is brought over the top of the pin 32 and thence sharply downwardly around the end 44 of the tensioner 38, considerable friction is placed upon the tape at this point. However, as the tensioner 38 is raised, the friction introduced at this point will be less because the tape 29 then will be brought over a smaller portion of the circumference of the pin 32 and will make a less sharp angle between the pin 32 and the lower end 44 of the tensioner. Therefore, :by proper adjustment of the tension introduced into the system by the springs 52, any tendency of the tape to resist movement through the machine to too great an extent will be accompanied Iby a slight lifting of the lower end 44 of the tensioner 38. This lifting will continue until the amount of tension introduced by the springs 52 is exactly balanced by the amount of drag on the lower end 44 of the tensioner by the tape passing therearound. The resistance cf movement of the tape through the machine or in other words, the tension effect which draws it snugly over the top of the knife edge 18 will therefore remain substantially constant even though the spool 28 changes in diameter as the tape is consumed. Further, radical changes in humidity which sometimes affect the characteristics of the tape will have very little effect upon the tension of the tape at the knife edge 18.

The tape which the specific machine here described is designed for and therefore the type which it is preferred to use is one made of paper having a white surface upon which black markings are made when heat is applied thereto. rllhis tape forms no part of the present invention but is available and usually comprises a paper base which is colored'black and upon which an extremely thin heat sensitive whitev surface is coated. The application 'of heat' breaks down the surface coating and exposes the black background. Inasmuch as the tape is drawn upon .by the ribbon of the stylus, which slides back and forth along the area where the tape passes over the knife edge 18, it will be seen that the arcuate motion of the tip end of the stylus will be converted into a straight line marking transversely Although photographic tape or tape which is drawn upon by a pen could be used in a machine of this type, the use'of a heat sensitive tape together with the heated stylus has the advantage of providing immediate markings, thus differing from the photographic tape which has to be developed. Also it 'Ls less messy and more quickly available for use than a pen and ink arrangement.

The rearward-edge of the vertical plate 22 carries a bracket |56 which extends to the right and is offset; somewhat toward the tape 29 and at its right hand end has a boss |512 which is drilled vertically to journal a shaft |54. rIhis vertical shaft may be rotated from side to side and at its upper end carries a second stylus |56 which is exactly similar to the stylus |40. The ribbon |48 of this stylus also rests upon the portion of the tape passing over the knife edge 48, but well toward one side thereof so that the markings made by this stylus are in the margin portion of A.9 the tape beyond the-central zone marked by-the stylus |40. The ribbon AM8 of this second stylus may be energized in parallel with the circuit which energizesthe stylus |49.

This second stylus, as will be pointed out in greater detail-presently, is for .the purpose of in ydicating to the operatorthat-the tape is not slipvfrom the number lconnection of the electrodes.

The mechanism'to be'described is so arranged as to shift this line It!) automatically so that it passes through dependingupon the electrode connections. Since there are four sets of numerals, positioning oi this line Vautomatically takes care ci four diiferent sets of electrodefconnections Occasion` ally still other arrangements are used in making an electrocardiogram and a scheme of coding these -additionalconnections is provided and will be described. In rthe interest of uniformity, this additional coding isdonenormally only when the line is in number 4 position.

An examination of the line |66 in Fig. 2 also shows evenly rspaced pips |52. These pipe are formed'in Ya manner -to be described by linkage to the driven rollerSiLthe roller making two pips for each revolution. Since this roller revolves at a rate of 30 R. P. it will be seen that the pips aremadeat the rate of one each second. Therefore, if the pips ISZIare-evenly spaced on the tape, it indicates that the tape has advanced an equal distance foreach second of operation and further, the heart rate may easily be determined lfrom the tape if desired.

The vertical shaft |54 and also the similar shaftf|38 projecting from the top or the galva-n noineter |36 have been described as being connected directly to the stylus. This is a satisfactory arrangement but it. requires that the pressure of the stylus ribbon n the tape be adjusted by springing the wires |56. In the interest of convenience in adjustment, the stylus is connected in each instance to the shaft in the following-manner. By reference to Figure it will be seen that the upper `end of the shaft itat above the boss |52 is divided with the two adjan cent vends oi` the shaft connectedto the tw@ arms of a U-shaped spring metal member iSd. This 'spring metal U-shaped piece is oriented with the U-bend toward the writing end of the stylus While the two free ends project some distance beyond the shaft |54 in the opposite direction. The two shaft members |54 may be connected to the spring metal member |645 in any suitable manner, such as by Swaging.

The lowerfarm of thespring metal member advjacent its free end is tapped to receive an adjusting screw |66 which extends through an opening in theupper leg of the U-shaped member such that, as the screw |66 is rotated from above with a screwdriver so that the 'thread advances into the tapped opening in the lower leg, .the head of the screw compresses the U-shaped spring metal member` thereby tilting the upper shaftportion |5|| relative to the lower vshaft portion..'l2he effect isto raise or decrease the pressure on 'the wrtingend of the stylus. Similarly,

the appropriate set ci. numerals point `204 to the mid point or" a backing oi the screw lowers the writing end of the stylus and increases `its pressure upon vthe tape.

The lower end of the shaft E54 below the bracket E50 is connected to a lever 68 which extends at approximately right angles to the-stylus in a direction toward and slightly beyond the vertical partition 22 and at its opposite vend is connected by a vertical pin Vit to a link |12, which extends toward the left behind the partition 22 where it is pivoted by `a horizontal pin llt to a vertical plate HG at a point near its upper edge. This plate llt is in turn pivoted by a horizontal pin il@ to a vertical lever at a below and to the left of the pin |`|8 as seen in Fig. 5. This and some of the last above described connections are better shown in Fig. 7 in which the left to right orientation is reverse since Fig. 'l shows the back oi the plate 22. Referring further to Fig. 7, the lever |89 extends approximately vertically and has its lower end pivoted by a horizontal pin |82 to the partition 22 some distance below the plate H5. The extreme right hand end of the plate ITG as seen in Fig. 7 is tapered so as to form athin extension or strip |855 at its top edge. This extension is bent at right angles to form a tab itt which extends through an opening |33 in the partition 22 above the motor shaft where its lower edge rides upon a cam itil iixed to rotate with the driving roll 8d. This cam is circular excepting that it has two oppositely disposed'notches itZ which allow the tab It to drop momentarily each half revolution of the driving roll 3|?, Close following ci the cam te@ by the tab |35 is insured by a coil tension spring it, one end oi which is hooked through a hole ist' in the lower leit edge (Fig. *7) of the plate llt while the other end is looped around the lower end oi the vertical pin |'||l which connects the lever l5@ to the link |12.

Now if it is assumed that the upper end of the lever it@ is held stationary, thereby fixing the pivot point |16, the periodic dipping ofthe tab |36 will pull upon the link Il?. `Since lthe link |12 is periodically jerked slightly to the right, as seen in Fig. 7, this in turn pulls the end of the lever |63 and rocks the shaft ld in a counterclockwise direction as seen from above. Theultimate result is to cause the stylus ribbon ltd to be jerked slightly toward the center of the tape momentarily, thereby producing the inwardly directed pips |62 previously referred to andillustrated in Fig. 2.

The upper end of thelever |80 is Ipivoted by a transverse horizontalpin |98 to a link 2519 vwhich extends generally horizontally to the right with a quarter twist therein, as seen in Figs. 5, l and 3.

The quarter twist in this link indicated at 202 is 'l simply iorthe purpose oi having the right hand portion of the link lie flat horizontally while the left hand portion thereof is in a verticalplane. This link 200 extends almost to the right hand end of the machine and there is pivoted by a pin horizontal lever 20B, one end of which is pivoted to a vertical pin EU8 fixed to one of the chassis members near the back thereof. In order to insure proper guidance for the link 202, it is provided with two longitudinal slots 2W and 2|2 spaced well apart which slip over vertical pins 2|4 and 2|6, respectively. This is best shown in 'Fig.'3. The outer end of the lever 206, that is the end toward the iront of the case, is pulled toward the left as seen in Fig. 3 by a coil spring 2 i8 hooked through a hole 220 in the lever 206 ina position somewhat for- 11 ward of the pin 204. The opposite end of this spring is secured by a screw 222 fixed in the chassis. The tendency therefore is for the lever 206 to be swung in a clockwise direction so as to push the link 20|) toward the left.

The extreme forward end of the lever 206 carries a vertical pin 224 with a small roller 226 journaled thereon as may be seen in Fig. 1. This roller presses against the edge of a disc cam 228 disposed to the left thereof and mounted upon the shaft 23|) of a rotary tap switch having a knob 232. This tap switch may be moved to any of a number of positions and when so moved serves to connect the several patient leads in various combinations. The specific switch and circuit for accomplishing this is not shown since it forms no part of the present invention and suitable circuits for this purpose will be apparent to anyone skilled in this art. So far as the present invention is concerned, it may be assumed that the switch, when rotated fully in a clockwise direction, comes against a stop and then when rotated in a clockwise direction, successively snaps to positions in which the patients leads are connected in combinations simply referred to for convenience as 1, 2, 3, 4 and others beyond 4.

When the above switch is backed off against its stop, the portion of the cam 226 farthest from the switch shaft 230 is brought into contact with the cam following roller 226. This is the calibrate position. When the tap switch is snapped from the calibrate position to the No. 1 position, the roller 226 still rides upon the portion of the cam 228 farthest from the center of rotation of the shaft 230. In these two positions, therefore, the end of the lever 206 nearest to the front of the case is as far toward the right as seen in Fig. 3 as it is under any conditions. The link 200 therefore may be considered as being pulled to its farthest right position. By referring to Fig. 7 in which the orientation is reversed, it will be appreciated that the link 200 there shown is pulled farthest to the left and that therefore the upper end of the lever |80 is the farthest to the left of any position it ever assumes. This brings about a general shifting of the plate |16 and link |12 toward the left (Fig. 7) with a consequent rocking of the lever |68 and shaft |64 in a clockwise direction as seen from above, which swings the stylus |56 and ribbon |48 carried thereby to the position shown by the line |60 in Fig. 2. That is with the line drawn nearest to the edge of the tape and so as to pass through numerals 1. This indicates to the operator, therefore, that the patients electrodes are connected in the No. 1 manner.

When the tap switch 232 is snapped to the No. 2 position, the cam 228 is shifted in a clockwise direction slightly so as to cause the roller 22 6 to drop against a portion of the cam indicated by the numeral 234 which is closer to the tap switch shaft 230. This causes the forward end of the shaft 206 to be moved somewhat to the left, as seen in Fig. 3, thereby carrying along with it the link 200 and the linkage connected thereto and just described in connection with the No. 1 position. Ultimately this causes the stylus ribbon |48 to be shifted inwardly somewhat so as to draw its line through the numerals 2. Additional inward steps 236 and 238 on the cam (Fig. 6) permit the cam follower 226 to move inwardly to the No. 3 and No. 4 positions as the rotary tap switch is swung to the No. 3 and No. 4 electrode combinations. This in turn causes the stylus to draw its line through the Nos. 3 or Nos. 4. The shape of the cam 228 is such that beyond the point 238 the cam surface is circular so that as the tap switch is moved beyond the No. 4 position, no movement of the stylus takes place. Conveniently, however, the cam surface can have an abrupt rise at 240 to serve as a stop to limit rotation of the cam when this abrupt rise is brought against the roller 226.

From the above, it will be seen that the tape is automatically coded for any combination of leads from l to 4. Additional coding beyond the No. 4 position is accomplished as follows, it being observed that the stylus position for combinations beyond tlie No. 4 position is such as to draw the line through the numerals 4. If desired, of course, an additional step on the cam could be used for shifting the stylus into a blank position inwardly of the numerals 4 on the tape although no sufficient advantage in doing this appears to justify such a provision. By referring to Figure 7, it will be seen that the left hand upper end of the plate |16 is provided with a tab 242 which would extend straight upwardly excepting that it is bent over at right angles so as to form a flat horizontal striker surface extending away from the partition 22. Directly above the striker surface 242 the cover plate of the instrument carries a downward extending tubular member 244 which houses a push rod 246, a portion of which extends above the upper end of the tubular member 242 to serve as a push button. The push rod 246 is somewhat shorter than the inside length of the tubular member 244, the lower end of which has an inwardly extending shoulder 248 through which a stem 250, smaller in diameter than the push rod 246, extends. Below the shoulder 248 the stem 250 is provided with a head 252 so as to form a second shoulder which is brought against the lower end of the tube 244 by a coil spring 254 housed within the lower portion of the tube. One end of this coil spring bears against the shoulder 248 while the other end presses upwardly against the lower end of the push rod 246 into which the upper end of the stem 250 is threaded. The lower end of the head 252 of the stem 250 is disposed just above the horizontal striker surface 242 at the end of the plate |16.

This arrangement is such it will be seen that the push rod 242 is normally urged to its uppermost position by spring 254 but when the upper end is depressed, it brings the head 252 against the striker surface 242 and urges it downwardly a short distance, thus rocking the plate |16 in a counterclockwise direction about the pivot point established by the pin |18. This pulls the link |12 toward the left as seen in Fig. 7 so as to swing the stylus ribbon |48 toward the margin of the tape shown in Fig. 2. In other words, whereas the notches |92 in the cam |90 rock the plate I 16 in a clockwise direction, thereby causing pips |62 which point inwardly on the tape, momentarily depressing the button 246 will similarly cause pips pointing outwardly.

If the operator therefore has taken all of the electrocardiograms that he desires with the electrodes connected in positions 1, 2, 3 and 4 and wishes to take an additional reading with some further combination of electrodes, he simply moves the rotary tap switch beyond the No. 4 position into a position giving a known combination of electrodes which is desired and then codes this particular connection by depressing the button 246 momentarily according to any code of his own choosing. In other words, he can use one or more short pips combined with 13 one `or. more long dashes which to him will-'signify whatever combination lof electrodes is being used.

As to details of mechanical construction, it will be seen by referring to Fig. l that the lever 266 is comprised of two strips arranged one above the other with the link 260 connected between. them. The two links 266 also embrace the two faces of the roller 226 previously mentioned, which is of smaller diameter than the width of the lever 266. inasmuch as the cam 226 is somewhat thinner than the roller 226, a portion of the edge of the cam 228 is overlapped on its top and bottom faces by the edges of the two strips 266. The roller 226 is therefore prevented from slipping off the face of the cam 226. Also, the pull upon the end of the link 266 by the pin 266 is in alignment with the centerof the roller 226, inasmuch as the strips *266 lie above and below the link 266 as well as above and below the roller 226. There is, therefore, no

Vtendency for looseness of either of the pins 264 `or 224 to permit deflection or bending of either to the side which could cause the position of the stylus ribbon |46 to give an inaccurate reading.

The driving roll 86 has been generally described and its use in the combination indicated.

lt may be formed and arranged in any suitable manner but the specific design used in the present apparatus is illustrated in Fig. 4. Here it will be seen that the shaft which extends from the electric motor and reduction gear drive vunit 82, extends into a sleeve indicated generally by the numeral 266. This sleeve has a cupshaped recess 262 in its opposite end tc take the cuter race of a lball bearing 26d. The inner race of this bearing is fitted to a stern 266, the outer end of which extends through the front L- shaped bracket 12 and is secured thereto by a nut 268. The sleeve 266 therefore is supported at its-outer end by the ball bearing 262 and stem 266, while its inner end is piloted upon the motor shaft 258.

Drive for the sleeve 266 is effected through one or more set screws 210 which extend radially 'throughthe sleeve 266 and bear against a flexible shaft 269. The flexible shaft 266 is crimped to a short length of tubing 215 which is splined to the'motor shaft 258. The result is that even though there is no perfect alignment between the z end of the motor shaft and the end of the sleeve l26!) carried thereby, nevertheless any weaving at this point will not loosen the driving connection 'between the'sleeve andthe motor shaft since the drive is transferred to the sleeve through the iiexible shaft 269. This sleeve is covered by a soft composition rubber coating 212 which forms the driving surface for the tape and this coating is relieved as at 21| over certain circumferential portions of its area in order to per- `mit tabs 216 formed at the end of the table |68 to be curved upwardly in the spaces provided by these relieved areas which prevent the tape passing rearwardly beneath the driving roll rather than across the table where it belongs. The circumference of the extreme inner end of the sleeve 260 is formed to provide the cam surface |66 previously referred to. Longitudinal position of the roller 86 on the shaft 256 is effected by means of a pair of C-shaped split rings 214 and 216 which are in face to face relation, one of these rings being snapped into a groove on the shaft 256, while the other ring 214 similarly snaps into a groove in a cup-shaped recess in the inner end of the sleeve 260.

`the other end which receives the pin |16. The

portion of the lever |66 which embraces the shaft |54 is therefore springy and forms a light friction nt therewith. The degree of friction between the lever |66 and the shaft |54 is adusted by a clamping screw 282 which extends transversely .through the two arms of the .lever at approximately its mid point. By tightening this screw the two arms embracing the .shaft |54 may be squeezed together so as to achieve rany Vdegree of friction desired.

`Normally the screw will be adjusted until it is tight enough to insure that no relative movement between the stylus shaft and the lever |66 will take place unless the stylus is grasped at a point close to the shaft |56 and twisted with the intention of purposely causing slippingbetween the shaft ifm and the lever |66.

Although the operation of the apparatus forming the subject matter of this invention has been described in detail as seemed appropriate along with the description of the various componente, a brief general description of its operation will n'ow be given.

When it is desired to place the apparatus in operation the detent it is depressed and a roll of tape slipped over the end of the tube 26. When the roll is in position the detent will snap outwardly and prevent the roll from being withdrawn accidentally. The knob |22 is then rotated ina clockwise direction as far as it will go, thereby moving the idling roll 64 away from lthe driving roll '80 while simultaneously liftingthe styluses |56 and N6 out of the way of the Ytape path. At this time also the tensioner i36v is raised away from the pin 62.

'with' the v guard`||2 in raised position. With the tape thus placed, the knob |22 is rotated in the counterclockwise direction so as to bring the idling roll 64| against the tape opposite the driving roll A86 while simultaneously lowering the tensioner 38 and styluses |46 and |66. Preferably then the motor 82 is switched on by whatever means is provided and runf or a period long enough to permit the tape to center itself in the driving mechanism. The lead selector switch 232 is then rotated as far as it will go in counterclockwise direction and the ribbon |28 of the stylus |56 is then checked to make sure that it is drawing its line through the numerals l. If not the stylus is grasped near the stylus shaft |54 and sprung one way or the other, thereby slipping the clutch connection between the lever |68 and the shaft |54 until proper positioning is achieved. If either of the styluses is not bearing against the tape with the proper pressure. the adjusting screw |66 of the particular stylus is rotated one way or the other to achieve this adjustment.

From this point onward as the machine is in operation the stylus ribbon |48 will draw a line through the appropriate set of numerals 1 to 4 to indicate the l to 4 positions of the tap switch knob 232 which in turn selects certain combinations of electrode connections to which these numbers are assigned. If any connections of electrodes in addition to those represented by the numerals 1 to 4 are desired, the tap switch knob 232 is turned to the appropriate position and additional code markings are made upon the tape by depressing the button 24S to form the desired number of outwardly directed pips in the line drawn by the stylus ribbon |40.

Meanwhile rotation of the driving roll 80 Will be accompanied by the formation of inwardly directed pips in the line drawn by the stylus ribbon |48 at the rate of one pip for each half revolution which in the present instance is one pip each second since the driving roll rotates at 30 revolutions per minute. While the instrument is operating, the galvanometer |36, which is connected to the electrocardiograph amplifier will, through the medium of the stylus |40, draw the characteristic electrocardiogram upon the central portion of the tape where it may easily be correlated with the trace drawn by stylus ribbon |48.

Although our invention has been described in connection with a specic embodiment thereof, it will be appreciated that additions thereto and variations therefrom may be made without departing from the scope of the invention.

Having described our invention, what we claim as new and useful and desire to secure by Letters Patent of the United States is:

1. In an electrocardiograph having tape pulling mechanism including a rotatable driving roll in frictional engagement with said tape for advancing said tape and switching means movable to a plurality of positions for connecting said electrocardiograph to a plurality of electrode combinations, means for indicating on said tape what combination of electrodes is connected to said electrocardiograph and also for recording indicia which indicates whether or not the tape is being advanced properly, the last said means including a stylus for drawing a line upon said tape, means connected to said switching means for changing the position of said stylus depending upon the position of said switching means so that said stylus draws a line in different positions on said tape depending upon the position of said switching means, and means actuated from the driving roll for momentarily disturbing the position of said stylus periodically as said driving roll rotates.

2. In an electrocardiograph having tape pulling mechanism including a rotatable driving roll in frictional engagement with said tape for advancing said tape and switching means movable to a plurality of positions for connecting said electrocardiograph to a plurality of electrode combinations, means for indicating on said tape what combination of electrodes is connected to said electrocardiograph and also for recording indicia which indicates whether or not the tape is being advanced properly, the last said means including a stylus for drawing a line upon said tape, means connected to said switching means for changing the position of said stylus depending upon the position of said switching means so that said stylus draws a line in different positions on said tape depending upon the position of said switching means, and means for momentarily disturbing the position of said stylus periodically.

3. In a recording instrument, tape advancing mechanism, a stylus and stylus actuating mechanism for drawing on said tape, movable switch means for connecting said stylus actuating mechanism to a plurality of stylus operating circuits, a second stylus for drawing on said tape, a member movable with said switch means, linkage means actuated by said movable member in some of its positions for changing the position of said second stylus according to the setting of said switch, manually actuated supplementary marking means for momentarily disturbing the position of the last said stylus at the will of the opcrater, and means for momentarily disturbing the position of the last said stylus according to uniform time intervals.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 745,240 Rolland, Jr Nov. 24, 1903 1,400,827 Leumann Dec. 20, 1921 1,839,608 Smith Jan. 5, 1932 1,910,361 Pick May 23, 1933 2,152,333 Spitzglass et al. Mar. 28, 1939 2,445,272 Keegan July 13, 1948 2,480,443 Branson Aug. 30, 1949 2,511,195 Buhrendorf et al. June 13, 1950 2,530,739 Stamper Nov. 21, 1950 2,577,950 `Clark Dec. l1, 1951 

